1. Field of the Invention
The present invention relates to a composition which is transparent and has a low coefficient of linear expansion, an optical element, a lens, and a method for manufacturing the composition.
2. Description of the Related Art
A cycloolefin polymer has features of high transparency and also low water absorptivity and is known to be useful as a material of optical elements, such as a lens. In contrast, it is also known that the cycloolefin polymer has a problem in environmental stability, e.g., when used alone, the cycloolefin polymer is likely to be thermally deformed. In particular, since it is assumed that the optical elements, such as a lens, are used in various temperature environments, it is suitable that the optical elements contain materials with high environmental stability which are difficult to be thermally deformed, i.e., materials having a low coefficient of linear expansion and the like.
Herein, in order to improve the environmental stability of the cycloolefin polymer, Japanese Patent Laid-Open No. 2007-91941 (hereinafter referred to as Patent Document 1) discloses an example of forming the cycloolefin polymer into a polymer alloy with a cross-linked product of a thermally cross-linkable compound of any one of an epoxy compound, an amino resin precursor, and an isocyanate compound.
According to the finding of the present inventors, since the compatibility of the thermally cross-linkable compound of any one of an epoxy compound, an amino resin precursor, and an isocyanate compound with the cycloolefin polymer is not high, it cannot be said that the transmittance of the polymer alloy is sufficient.